The present invention relates generally to transmission gear assemblies, and is particularly concerned with a variable gear assembly for producing a variable transmission ratio.
Gear assemblies are known which have a constant angular velocity or transmission ratio for transmitting power from one shaft to another shaft. These gear assemblies have two gears of constant diameter which are in meshing engagement via teeth or the like. U.S. Pat. No. 5,247,847 of Gu describes a cam gear assembly in which a cam gear of a first, constant diameter has a series of teeth defining a lobular periphery and a roller gear of a second, constant diameter is in meshing engagement with the cam gear. Both gears are of constant diameter. The roller gear has a plurality of rotatably mounted rollers around its perimeter for meshing engagement with the gear teeth, and the second diameter is smaller than the first diameter. This provides a constant angular velocity ratio. The provision of a roller gear instead of mating conventional gears with meshing teeth reduces the risk of damage to the gear teeth and possible failure of the transmission.
Variable ratio gear transmissions employ at least one pair of non-circular gears to provide a continuously variable transmission ratio. One such variable gear arrangement is described in U.S. Pat. No. 4,685,348 of Takami. At least one pair of non-circular gears have intermeshing gear teeth to produce a continuously variable transmission. U.S. Pat. Nos. 5,381,766 and 5,405,300 of Sakita describe a rotary piston engine in which piston assemblies are connected to the engine output shaft through non-circular gear sets. Each non-circular gear set includes a heart shaped gear and a teardrop shaped gear with intermeshing teeth. The teeth on the teardrop shaped gear may be replaced with rollers. However, this gear has a relatively large number of rollers and the engagement of the rollers in the recesses between adjacent teeth may give rise to some instability.